The invention relates to residential branch circuit breakers, which are the molded case, narrow width type, usually 1 inch or 3/4 inch, such as shown in U.S. Pat. No. 3,081,386. These breakers are normally utilized in residential and commercial applications up to 240 volts.
Circuit breakers, and the panelboards or load centers to which they are mounted, are designed to be compact and physically compatible with existing apparatus. However, electrical utilities are providing increased available current in new installations. As a result, the short circuit interruption capacity requirement of narrow width circuit breakers has increased from 10,000 amps to 22,000 amps for new breaker designs, while existing apparatus designs place severe limitations on changes in physical arrangement and size.
Together with the high capacity requirement, there is an on-going need to dissipate and extinquish the arc between separating contacts. Furthermore, the arc debris must not be allowed to accummulate or otherwise interfere with the contacts or with operating mechanisms.
These requirements must be met within the narrow width case of residential branch breaker. In contrast, industrial breaker designs do not have such size constraints, and their much higher current interruption capacity involves different design criteria.
The present invention provides a residential breaker incorporating a combination slot motor and arc chute. The combination slot motor and arc chute concentrates the magnetic repulsive force between current carrying conductors to boost contact separation force, and also extinguishes the arc. The slot motor portion of the combination structure continues to support the magnetic force which tends to force the arc into the arc chute portion away from the contacts and operating mechanism.
The combination slot motor and arc chute is particularly simple and inexpensive, but very effective. Increased short circuit interruption capacity, and clensing arc blow out and dissipation, are provided without resorting to wide case design or otherwise resorting to industrial breaker type design.